1. Technical Field
This application relates generally to magnetic recording heads, particularly to the design of magnetic shields that restrict the magnetic write field to tracks being written on and eliminate adjacent track erasures (ATE).
2. Description of the Related Art
The increasing need for high areal recording densities (□750 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head). By means of fringing magnetic fields that extend between two emerging pole pieces, a main pole (MP) and a return pole, magnetic recording heads form small magnetic domains within the surface plane of the magnetic medium (hard disk). As recorded densities increase, these domains must correspondingly decrease in size, eventually permitting destabilizing thermal effects to become stronger than the magnetic interactions that tend to stabilize the domain formations. This occurrence is the so-called superparamagnetic limit. Recording media that accept perpendicular magnetic recording, allow domain structures to be formed perpendicularly to the disk surface and a soft magnetic underlayer (SUL) formed within the medium acts as a stabilizing influence on these perpendicular domain structures. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to the disk surface, when used in conjunction with such perpendicular media, is able to produce a stable recording with a much higher area density than is possible using standard longitudinal recording.
A significant problem with magnetic pole structures that are currently used to produce perpendicular fields, is that the fields tend to exhibit significant lateral (cross-track direction) fringing, thereby producing unwanted erasures in tracks adjacent to those actually being written on, called “adjacent track erasure” (ATE). If the erasures extend beyond those tracks adjacent to the track being written on, creating a wide area of erasures, the effect is called “wide area track erasure” (WATE). Moreover, these two effects are exacerbated by high-frequency magnetic fields, which will make them an increasing problem in high data-rate recording. The traditional approach to restricting the extent of the fringing magnetic field to only those areas on which writing is desired, is to surround the emerging tip of the main pole with magnetic shields. These shields are formed of magnetic material and, in various configurations, may surround the pole tip at its top and bottom (in a down-track direction) and/or at its sides (in a cross-track direction).
Two views of a common shielded pole fabrication can be seen by referring to FIGS. 1 and 2. FIG. 1 is a schematic view through the ABS plane of the shielded pole structure as it appears when formed, as part of the PMR head (nominally called the “front” of the head) showing, in cross-section, a substrate (5), the beveled pole tip (10), two opposing side shields (20) laterally disposed about the pole tip and an upper shield (40) formed above the pole. The rear portion of the pole is not seen in this figure, but is seen (as (27)) in the overhead view of FIG. 2.
FIG. 1 also shows a horizontal write gap layer (50) preferably formed of alumina, and, typically, alumina side gap insulating layer (60) surrounding the pole. As can be seen, the facing surfaces (25) of the two side shields are slanted in such a way as to form a truncated wedge-shaped opening, widest at the upper shield surface, within which is formed the beveled pole tip. In this common structure, the side shields are formed of homogeneous magnetic alloys, such as NiFe alloy.
Referring now to FIG. 2, there is shown an overhead cross-sectional view through a horizontal plane of the fabrication of FIG. 1, taken at a level through the central plane of the main pole. Because of the position of the plane through the main pole, the upper shield is not shown. Two separated side shields (20) are seen laterally disposed about the pole tip (10). The main pole flares laterally (26) in a direction away from the ABS. In this typical configuration, the side shields will be formed of a homogeneous magnetic material such as a nickel-iron (NiFe) alloy and, typically, these shields would be plated and then shaped appropriately by a method such as reactive-ion etching (RIE).
Unfortunately, it has been found that side shields formed of a homogeneous plated magnetic alloy, as illustrated in FIG. 2, do not provide sufficient lateral shielding to prevent ATE and WATE when the writer operates at high-frequencies. Although there have been attempts to address the problem, such as taught by:    U.S. Patent Application 2010/0033879 (Ota et al),    U.S. Pat. No. 7,983,009 (Ota et al) and    U.S. Patent Application 2007/0268623 (Feng),
These teachings do not provide the advantageous results of the present disclosure, specifically lacking the capability of meeting the objects described in the summary below.